diff --git a/addons/stock/wizard/stock_lot_label_layout.py b/addons/stock/wizard/stock_lot_label_layout.py
index 4898008e09b..4e09072d233 100644
--- a/addons/stock/wizard/stock_lot_label_layout.py
+++ b/addons/stock/wizard/stock_lot_label_layout.py
@@ -36,7 +36,7 @@ class ProductLabelLayout(models.TransientModel):
                     quantity_by_lot[move_line.lot_id.id] += 1
             docids = []
             for lot_id, qty in quantity_by_lot.items():
-                docids.append([lot_id] * qty)
+                docids.extend([lot_id] * qty)
         report_action = self.env.ref(xml_id).report_action(docids, config=False)
         report_action.update({'close_on_report_download': True})
         return report_action